The invention relates to an air spring having a cover, a base element and having flexible bellows which are clamped in a pressure-tight fashion between the latter, and having a level-measuring device which is integrated at least partially into the bellows and has the purpose of sensing the level of the air spring.
In order to ensure that there is an identical setpoint level of the body in different load states in vehicles with an air spring device and air springs, a means for regulating the level of the body is present. For this purpose, knowledge of the actual level of the vehicle body or of the level of the air springs arranged between the vehicle body and the axles is necessary, level-measuring devices which are integrated into the air bellows being known from the prior art because of a certain lack of sensitivity for external conditions and for ease of mounting.
DE 10 2008 028 916 B4 proposes a device for sensing a level of bellows in which a sensing device is arranged in the interior of the air bellows, which device senses the position of a rolling fold of the air bellows which is formed on the outside of the air bellows, and modulates a position-dependent signal. It is disadvantageous that the formation of the rolling fold does not necessarily behave linearly with spring compression and that, owing to the external sensing of the rolling fold, sealing problems can occur at the air bellows.
DE 100 17 562 C1 proposes a height sensor which is integrated into the air bellows and has a length-variable winding and a coil. An alternating voltage is applied to the coil, which also brings about an induced electrical voltage in the winding owing to the magnetic field which is generated as a result. This voltage is evaluated in an evaluation unit and forms a measure of the distance of the cover from the piston.
DE 10 2008 028 917 B4 proposes a device for sensing a dynamic change in pressure in the air spring during spring compression, wherein the level is determined as a function of the static pressure and the dynamic change in pressure.
DE 40 35 784 A1 proposes coil-shaped conductive conductor tracks in the wall of the air spring bellows of an air spring. In this context, in the case of spring compression, a change in the inductance of these coil-shaped conductor tracks is evaluated electronically, and the spring compression is determined on the basis thereof.
However, the abovementioned approaches have disadvantages with respect to general conditions such as severely changing temperatures, oil-containing and particle-containing surroundings, pressure fluctuations, tight installation space, reproducibility, etc.
In view of the above, the invention is based on the object of making available an air spring having a level-measuring device which is integrated at least partially into the bellows, wherein precise measurement of the level can take place in the simplest and most robust way possible.
According to the invention, the level-measuring device includes:                at least one angle sensor which is integrated into the bellows and which is connected at least in a rotationally fixed fashion to the cover or to the base element and has an element which can rotate with respect to a base,        a mechanical coupling which is connected, on the one hand, to the rotatable element of the angle sensor and, on the other hand, to the cover or to the base element such that when the level of the air spring changes, an angle of at least one element of the mechanical coupling is changed, and the angle sensor generates an angle signal which is dependent on the change in angle of the element, and        an evaluation device by which the angle signal which originates from the angle sensor is assigned to a level of the air spring.        
In other words, a change in the vertical relative level positions of the cover and the base element by way of the kinematics of the mechanical coupling between the rotational angle sensor and the cover or base element is converted into a change of the angular position of the rotatable element of the angle sensor. The result is that the respectively assumed angular position of the rotatable element forms a measure of the spring compression or spring extension or of the change in length of the air spring.
The at least rotationally fixed connection of the angle sensor to the cover or to the base element therefore has its rotational rigidity with respect to a rotational axis of the rotatable element of the rotational angle sensor.
Such determination of the level which is made by way of a mechanical coupling between the rotational angle sensor and the cover or the base element is robust since it is relatively insensitive to changes in temperature, for example. There is also a certain degree of insensitivity to an environment containing oil or particles. However, it is decisive that each determined rotational angle or pivoting angle of the rotatable element of the angle sensor can be assigned a uniquely defined level of the air spring.
According to the invention, the term “level” is understood to mean: (i) the distance of the cover from a surface, lying opposite, of the base element of the air spring (for example, a piston face of a piston), (ii) the length of the air spring viewed in the direction of a vertical central axis of the air spring, or (iii) a distance of an axle of a vehicle from the vehicle body, depending on which of the specified variables appears more suitable for further use, for example within the scope of a level-regulating algorithm.
In this context, the evaluation device can be arranged inside or outside the air spring or the bellows.
Advantageous developments and improvements of the invention are described and claimed herein
According to one preferred embodiment, the mechanical coupling contains at least one element which is guided in a sliding fashion by one of its ends in a guide on the base element or on the cover and is connected by its other end to the rotational element of the angle sensor, in such a way that when the level of the air spring changes, the one end of the element is moved along the guide, and the other end activates the rotational element of the angle sensor. In this context, the guide can be a linear longitudinal guide which is arranged in a plane perpendicular to a central axis of the air spring.
This embodiment is advantageous in terms of its robustness, because it can be implemented very easily with just a single rod-shaped element, in particular if the guide is a sliding guide.
According to a further embodiment, the mechanical coupling contains a scissor mechanism, with at least two scissor elements which are connected to one another in an articulated fashion. One end of a first scissor element is connected to the rotational element of the angle sensor, and one end of a second scissor element is coupled via a linkage to the base element or to the cover in such a way that when the level of the air spring changes, the scissor mechanism lengthens or shortens in the direction of the central axis of the air spring, and the second scissor element rotates about the linkage, and the first scissor element activates the rotational element of the angle sensor. In this context, the scissor mechanism can contain intersecting and/or non-intersecting scissor elements.
According to a further embodiment, the mechanical coupling contains a telescopic device which is coupled by one of its ends to the cover or to the base element by way of a linkage and is connected by its other end to the rotational element of the angle sensor in such a way that when the level of the air spring changes with lengthening or shortening of the telescopic device, the one end rotates about the linkage and the other end activates the rotational element of the angle sensor. In this context, the telescopic device can contain at least two telescopic elements which can be slid relative to one another with a longitudinal degree of freedom.
The advantage of this embodiment is, in turn, the simplicity of its design with at minimum only two telescopic elements which can be slid in one another or on one another, and just one linkage to the cover or to the base element.
The evaluation device is particularly advantageously integrated into the bellows and arranged on the cover. The evaluation device is then also accommodated in a way which is protected against outside influences such as dirt and moisture. Furthermore, the air spring then forms, together with the assigned level-measuring device, a unit which is ready for installation and easy to mount.
The angle sensor can be placed at any desired position in the interior of the bellows and can be adapted to the conditions of the mechanical coupling. In particular, the angle sensor is arranged centrally or eccentrically with respect to a central axis of the air spring.
The rotational element of the angle sensor can interact in a contactless fashion or by way of contact with the base. An example of an interaction of the rotational element with the base by way of contact is a rotational potentiometer in which the rotational element is composed of a rotational slide which interacts with a conductor track and in which the electrical resistance changes in a measurable fashion with the rotational angle. Examples of contactless interaction of the rotational element with the base are a Hall element, inductive rotational angle sensor and rotational angle sensor according to the incremental transmitted light method.
According to one development, the rotational axis of the rotational element of the rotational angle sensor can be arranged perpendicular with respect to a plane which contains the central axis of the air spring.
The invention also relates to an air suspension device for a vehicle containing at least one air spring as described above.
In such an air suspension device for a vehicle a valve arrangement is then provided by which a pressure medium is fed to or discharged from the bellows of the air spring as a function of the determined level of the at least one air spring, in order to set a predefined setpoint level. This valve arrangement is then controlled by an electronic level-regulating system.
Advantageous developments of the invention can be found in the patent claims, the description and the drawings. The advantages of features and of combinations of the plurality of features as specified in the introduction to the description are merely by way of example and can be effective alternatively or cumulatively without the advantages necessarily having to be achieved by embodiments according to the invention. Further features can be found in the drawings, in particular the illustrated geometries and the relative dimensions of a plurality of components with respect to one another and their relative arrangement and operative connection. Features of different embodiments of the invention or features of different patent claims can also be combined in a way which differs from the selected back-references of the patent claims, and are suggested herewith. This also relates to such features which are illustrated in separate drawings or mentioned in the description thereof. These features can also be combined with the features of different patent claims. Likewise, features which are disclosed in the patent claims can be omitted from other embodiments of the invention.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.